When producing hydrocarbons from a well it is preferable to have knowledge of physical parameters of relevance to how the well is producing. Physical parameters can be measured at the wellhead, but it is strongly preferable to be able to take measurements into the well, preferably in production zones of the well.
Pressure is particularly interesting, but also many other physical parameters are of interest, such as temperature, composition and flow rates. Further, it can be of major interest to have valves, pumps or other means that require power and signals from the surface installed into the well.
In patent publication U.S. Pat. No. 6,644,403 B2 a method and a device are described for the measuring of physical parameters in a production well. Into the well, in an annulus between a production pipe and an exterior casing, a half-transformer is arranged in the annulus and a half-transformer is arranged in the production pipe. The half-transformer in the annulus has electrical connection by means of cables to the surface of the well. The half-transformer inside the production pipe is inductively coupled to the outer half-transformer and has connection to at least one sensor, an element for storage of energy, and electronic circuits, arranged inside the production pipe. The equipment situated in the annulus is permanently installed, while the equipment situated inside the production pipe can be replaced by light well intervention, such as by cable operations. Thus, the invention according to U.S. Pat. No. 6,644,403 B2 provides advantage by allowing for equipment arranged inside the production pipe to be replaced without comprehensive operations in the well being required.
In patent publication U.S. Pat. No. 6,515,592 B1 different methods and devices are described to send at least one electrical signal to or from at least one downhole device in a well. The downhole installed devices are permanently installed. Current is directed into a casing by use of a source at the surface connected to the casing. One or several permanent downhole devices are electrically connected to the casing, and the electrical connection to the casing is used to provide power to the downhole devices. The downhole devices also send out a signal to the isolated casing that can be directed via the casing to a surface-located receiving unit that receives and stores signals. The upper part of the casing closest to the surface is electrically insulated from the underlying part, and direct or inductive electrical connection is arranged from the surface unit to the underlying part. In the casing insulating gaps are provided, and underlying casing is connected by means of an electrical cable with a primary coil. A secondary coil with connected downhole devices are inductively coupled to the primary coil. In one embodiment effect and signal are passed down through an inner pipe and back through an outer pipe. Power and signals are sent to and from the permanently located downhole device by use of distinct frequencies and/or addressing. There is no description of inductive coupling to an inner production pipe, there is no description of measuring devices inside the inner pipe, and there is no description of short-circuiting between the outer and inner pipe in the upper end of a well, else than through a surface located generator/signal unit.
In patent application publication US 2004/0144530 A1 a ferromagnetic reactance-providing enveloping device and use thereof in a petroleum well are described, by which a voltage drop is developed over the reactance-providing enveloping device when an alternating current is passed through an interior pipe, and effect and signals are thereby taken out, used to drive and communicate with devices and sensors in the well. The reactance-providing enveloping device, a so-called choke, do not receive power and is prepared from a material having high relative magnetic permeability, for example in the range of 1,000 to 150,000, such as a ferromagnetic metal alloy or a ferrite. The choke is electrically isolated from the interior pipe and acts to provide a reactive impedance against the alternating currents in the pipe. The power and signal source at the surface is not inductively coupled to the well.
In patent publication U.S. Pat. No. 6,684,952 B2 a method and an apparatus are described, providing communication of electrical power and signals from downhole components to other downhole components, by use of an inductively coupled assembly. Concentric side-by-side primary and secondary coils are used, having connection from the surface through a cable to a primary coil close to equipment for measurement and/or control. More specifically, feedthrough of power and electrical signals through a liner/casing-wall without electrical leadthroughs is described, by the use of inductive coupling.
A demand exists for further development of the above-mentioned prior art, for implementation in a well without use of long cables, and with possibility for replacement of sensors and other sensitive equipment situated inside a production pipe. A particular demand exists for technology useful in wells that are short-circuited between the production pipe and the casing at the surface, with a hanger where said pipes are hung up, and short-circuited down into the well with a packer between said pipes, and particularly for connection to zones and equipment located further down into the well than the short-circuiting packer.